Pulsars, or neutron stars, are the universe's densest objects other than black holes. Special pulsars known as magnetars can have intense magnetic fields up to a trillion times stronger than our Sun...but one strange magnetar has been hiding its powers.

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All neutron stars are incredibly dense and incredibly magnetized - they pack the mass of the Sun into a sphere only a couple dozen miles in diameter, and they have magnetic fields billions of times greater than that of the Sun. But magnetars are even more intensely magnetized, anywhere from 50 to 1000 times the strength of normal pulsars, and as a result they constant emit powerful bursts of gamma rays and X-rays.

Amazingly, even if the surface magnetism of a magnetar is a trillion times that of the Sun, the interior magnetism will be even stronger, which causes the crust of the star to heat up and particles to accelerate, which is what causes the energy blasts.

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Such activities were thought to be exclusive to magnetars, but now an apparently weaker pulsar has been spotted doing its best impression of a magnetar. The neutron star SGR 0418 shows no evidence of a powerful external magnetic field, and yet it is constantly emitting powerful bursts and flares, just like a magnetar would. The only possible explanation is that it has an internal magnetic field that is perhaps millions of times more powerful than the surface magnetism.

Indeed, the difference between the intensity of the external and internal magnetic fields is of huge importance to understanding how this pulsar works. As lead researcher Dr. Silvia Zane explains, the Chandra X-ray observatory should be able to figure out the maximum difference between the two fields. If the upper limit is too low, she says, then SGR 0418 will become a real mystery:

"It is the very first time this has been observed and the discovery poses the question of where the powering mechanism is in this case. At this point, we are also interested in how many of the other normal, low field neutron stars that populate the galaxy can at some point wake up and manifest themselves as a flaring source. If further observations by Chandra and other satellites push the surface magnetic field limit lower, then theorists may have to dig deeper for an explanation of this enigmatic object."